There is increasing emphasis for wireless communication systems to provide higher data rates so as to allow for increased throughput. In this regard, Long-Term Evolution (LTE) and LTE-Advanced systems have been developed so as to provide enhanced services including higher data rates and reduced latency at lower cost.
In LTE environments various uplink methods are used, for example as is described in Section 8.6 of 3GPP specification TS 36.213, which is hereby incorporated by reference as if set forth in its entirety herein, an LTE uplink such as a Physical Uplink Shared Channel (“PUSCH”) generally carries only Uplink Control Information (UCI) (i.e., no data). For example, when a mobile terminal detects that certain reserved Modulation and Coding Scheme (MCS) levels are indicated by an uplink (UL) grant and when the total number of assigned Physical Resource Blocks (PRBs) fulfills a certain requirement, the mobile terminal may utilize UCI-only PUSCH.
It has been shown that with configured component carriers (CCs) and a Channel State Information (CSI) feedback mode 3-1, a typical example of UCI feedback overhead would be 5 CC×68 bits/CC=340 bits. In LTE release 11, with the introduction of downlink (“DL”) coordinated multiple point transmission/reception (“CoMP”), it is possible that one mobile terminal could be configured to report the UCI corresponding to a set of N cells/points. The worst case would be that the payload size will be increased to N*340 bits, with 5 configured CCs and N configured cells/points all requiring a UCI report. In this case, it is useful to allow 16-quadrature amplitude modulation (“QAM”) and/or rank-2 transmissions for higher spectrum efficiency.
Existing proposals for modulation scheme and rank indication for UCI-only PUSCH fall short of achieving the desired higher spectrum efficiency. One example is modulation scheme indication using quadrature phase shift keying (QPSK) or 16 QAM. In this example, if UCI reporting is triggered by DCI format 0: (a) whether QPSK or 16 QAM is used can be implicitly indicated by the number of CCs that are configured for UCI report, e.g., 16 QAM is used when more than two CCs require UCI feedback; and (b) whether QPSK or 16 QAM is used can be explicitly indicated by a reserved MCS stage, e.g., I_{MCS}=31. In another example, if UCI reporting is triggered by DCI format 4: (a) whether QPSK or 16 QAM is used can be implicitly indicated by the number of CCs that are configured for UCI report; (b) whether QPSK or 16 QAM is used can be explicitly indicated by a reserved MCS stage, e.g., I_{MCS}=31; and/or (c) whether QPSK or 16 QAM is used can be explicitly indicated by the NDI field of a disabled TB=1. Another example is Rank indication, such as rank1 or rank 2. Assuming that for the case of rank 2, a single codeword (CW) is mapped to two layers; UCI reporting is triggered by downlink control information (DCI) format 4 and/or one of the two TBs is disabled; and/or PMI field indicates the rank 2 precoder.